Deposition of undesirable materials can be detrimental to the efficient operation of paper or pulp mills. Deposition problems in the dryer section of a paper or pulp mill result when paper, paperboard, or market pulp is made from a pulp furnish which contain materials that, due to their hydrophobic nature, have a tendency to be tacky at the dry end of the paper machine. These tacky materials may be picked out of the paper web due to adherence directly to the dryer cans. In a similar dry environment, these materials may be picked out of certain press rolls. Aggregates of these materials can also be transferred from the press section to the sheets and be redeposited in the dryer section. Deposits in a paper machine dryer section may occur on the dryer can surfaces as well as the dryer fabrics and the dryer fabric carrier rolls. Dryer section deposits can be costly as they cause sheet defects such as holes, spots and coating streaks. The deposits can also cause lost production time due to the need for excessive equipment and dryer fabric cleanup. In severe cases, the costly dryer fabrics will need to be replaced prematurely. Current treatments for dryer deposit control have met with limited success.
Materials which may be tacky in the dry end of a paper machine can include processing aids such as antifoams and sizing agents, natural resins such as wood pitch, as well as materials added to paper to improve its function (coatings, glues, etc.) which end up in the paper making process when these papers are reused. Deposits which occur when papers are reused are commonly referred to as white pitch and stickies. The problem of white pitch deposition occurs when coated paper is reused. Coatings generally comprise (1) latex, generally styrene butadiene (SBR) and/or polyvinyl acetate (PVAC), (2) binders such as starch, casein, polyvinyl alcohol, etc., and (3) inorganic pigments, usually clay, calcium carbonate and titanium dioxide.
The problem of stickies deposition occurs when paper or paperboards are recycled which contain materials such as (1) labels and envelopes with adhesives such as SBR and vinyl acrylates, (2) books and magazine bindings containing hot melt glues such as vinyl acetate polymers, and (3) produce boxes with wax or polyethylene coatings or (4) materials which contain packing tape. Dryer section deposition occurring from these sources may or may not also contain natural wood pitch components such as fatty esters and fatty acids or sizing agents such as rosin, alkenylsuccinic anhydride, or alkyl ketene dimer.
Various methods of controlling deposits in papermaking systems are known. U.S. Pat. No. 4,886,575, December 1989 to Moreland discloses the use of certain types of polyvinyl alcohol for detackification of adhesive materials in secondary fiber. U.S. Pat. No. 4,871,424, October 1989 to Driesbach et al., teaches the use of certain types of polyvinyl alcohol for controlling natural wood pitch deposition. In both cases, detackification of the specific tacky material was for deposition control on all equipment surfaces throughout the papermaking environment.
U.S. Pat. Nos. 4,698,133 October 1987 and 4,781,794 November 1988 to Moreland teach the use of a methyl ether cellulose derivatives for detackification of adhesive material in secondary fiber to decrease deposits in a papermaking environment.
U.S. Pat. No. 4,686,119, August 1987 to Nojima et al., teaches a method of producing cast coated paper wherein a releasing agent is included in the coating formulation in order to decrease the sticking of the coating to the drum of the cast coater. The release agents were selected from the group of a phosphates having a fatty hydrocarbon radical with 6 to 20 carbon atoms, and amine salts thereof and lecithin which includes synthetic phosphatidyl chlorine derivatives. U.S. Pat. No. 4,857,126 August 1989 to Soremark et al., teaches a process for improving the release of wet coated paper from coating rolls to improve the appearance of the coated surface. The method utilizes a release agent comprising equal molar amounts of an alkanolamine and a fatty acid. The release agent is added directly to the coating formulation.